<?php

// +----------------------------------------------------------------------

// | ThinkPHP [ WE CAN DO IT JUST THINK IT ]

// +----------------------------------------------------------------------

// | Copyright (c) 2009 http://thinkphp.cn All rights reserved.

// +----------------------------------------------------------------------

// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )

// +----------------------------------------------------------------------

// | Author: liu21st <liu21st@gmail.com>

// +----------------------------------------------------------------------

namespace Think\Crypt\Driver;

/**

 * Base64 加密实现类

 */

class Base64 {



    /**

     * 加密字符串

     * @param string $str 字符串

     * @param string $key 加密key

     * @param integer $expire 有效期（秒）     

     * @return string

     */

    public static function encrypt($data,$key,$expire=0) {

        $expire = sprintf('%010d', $expire ? $expire + time():0);

        $key    =   md5($key);

        $data   =   base64_encode($expire.$data);

        $x=0;

		$len = strlen($data);

		$l = strlen($key);

        for ($i=0;$i< $len;$i++) {

            if ($x== $l) $x=0;

            $char   .=substr($key,$x,1);

            $x++;

        }



        for ($i=0;$i< $len;$i++) {

            $str    .=chr(ord(substr($data,$i,1))+(ord(substr($char,$i,1)))%256);

        }

        return $str;

    }



    /**

     * 解密字符串

     * @param string $str 字符串

     * @param string $key 加密key

     * @return string

     */

    public static function decrypt($data,$key) {

        $key    =   md5($key);

        $x=0;

        $len = strlen($data);

        $l = strlen($key);

        for ($i=0;$i< $len;$i++) {

            if ($x== $l) $x=0;

            $char   .=substr($key,$x,1);

            $x++;

        }

        for ($i=0;$i< $len;$i++) {

            if (ord(substr($data,$i,1))<ord(substr($char,$i,1))) {

                $str    .=chr((ord(substr($data,$i,1))+256)-ord(substr($char,$i,1)));

            }else{

                $str    .=chr(ord(substr($data,$i,1))-ord(substr($char,$i,1)));

            }

        }

        $data = base64_decode($str);

        $expire = substr($data,0,10);

        if($expire > 0 && $expire < time()) {

            return '';

        }

        $data   = substr($data,10);

        return $data;

    }

}